H3C S5100-SI Operation Manual page 397

Local precedence is a locally significant precedence that the switch assigns to a packet. A
local precedence value corresponds to one hardware output queue on the egress port.
Packets with the highest local precedence are processed preferentially. As local
precedence is used only for internal queuing, a packet does not carry it after leaving the
queue.
4) Drop precedence
Drop precedence is used for making packet drop decisions. Packets with the highest drop
precedence are dropped preferentially.
Priority trust mode
A switch can assign different types of precedence to received packets as configured, such
as 802.1p precedence, DSCP values, local precedence, and drop precedence.
The S5100-SI series switches do not support marking drop precedence for packets.
1) For an 802.1q-untagged packet
When a packet carrying no 802.1q tag reaches a port, the switch uses the port priority as
the 802.1p precedence value of the received packet, searches for the set of precedence
values corresponding to the port priority of the receiving port in the
802.1p-precedence-to-other-precedence mapping table, and assigns the set of matching
precedence values to the packet.
2) For an 802.1q-tagged packet
For incoming 802.1q tagged packets, you can configure the switch to trust packet priority
with the priority-trust command or to trust port priority (the default). The priority mapping
process is as shown in Figure 1-5.
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